Abstract [en]

The emerging field of organic electronics is heralded because it promises low-cost and flexible devices, and it was recently demonstrated that a light-emitting electrochemical cell (LEC) can be fabricated with cost-efficient methods under ambient air. However, the LEC turns sensitive to oxygen and water during light-emission, and it is therefore timely to identify flexible encapsulation structures. Here, we demonstrate that a multilayer film, featuring a water and oxygen barrier property of ≈1 × 10–3 g/m2/day and ≈1 × 10–3 cm3/m2/bar/day respectively, is fit for this task. By sandwiching an LEC between such multilayer barriers, as attached by a UV-curable epoxy, we realize flexible LECs with performance on par with identical glass-encapsulated devices, and which remain functional after one year storage under air.

In thesis

Asadpoordarvish, Amir

Umeå University, Faculty of Science and Technology, Department of Physics.

2015 (English)Doctoral thesis, comprehensive summary (Other academic)

Abstract [en]

The introduction of artificial illumination has brought extensive benefits to mankind, and during the last years we have seen a tremendous progress in this field with the introduction of the energy-efficient light-emitting diode (LED) and the high-contrast organic LED display. These high-end technologies are, however, produced using costly and complex processes, and it is anticipated that the next big thing in the field will be the advent of a low-cost and “green” illumination technology, which can be fabricated in a cost- and material-efficient manner using non-toxic and abundant raw materials, and which features attractive form factors such as flexibility, robustness and light-weight. The light-emitting electrochemical cell (LEC) is a newly invented illumination technology, and in this thesis we present results that imply that it can turn the above vision into reality.

The thin-film LEC comprises an active material sandwiched between a cathode and an anode as its key constituent parts. With the aid of a handheld air-brush, we show that functional large-area LECs can be fabricated by simply spraying three layers of solution -- forming the anode, active material, and cathode -- on top of a substrate. We also demonstrate that such “spray-sintered” LECs can feature multicolored emission patterns, and be fabricated directly on complex-shaped surfaces, with one notable example being the realization of a light-emission fork!

Almost all LECs up-to-date have been fabricated on glass substrates, but for a flexible and light-weight emissive device, it is obviously relevant to identify more appropriate substrate materials. For this end, we show that it is possible to spray-coat the entire LEC directly on conventional copy paper, and that such paper-LECs feature uniform light-emission even under heavy bending and flexing.

We have further looked into the fundamental aspects of the LEC operation and demonstrated that the in-situ doping formation, which is a characteristic and heralded feature of LECs, can bring problems in the form of doping-induced self-absorption. By quantitatively analyzing this phenomenon, we provided straightforward guidelines on how future efficiency-optimized LEC devices should be designed.

The in-situ doping formation process brings the important advantage that LECs can be fabricated from solely air-stabile materials, but during light emission the device needs to be protected from the ambient air. We have therefore developed a functional glass/epoxy encapsulation procedure for the attainment of LEC devices that feature a record-long ambient-air operational lifetime of 5600 h. For the light-emission device of the future, it is however critical that the encapsulation is flexible, and in our last study, we show that the use of multi-layer barrier can result in high-performance flexible LECs.